A damper is built in a front fork of a two-wheel vehicle and adjusts a damping force by a motor. JP2008-14431 discloses a damper including a damper main body with a cylinder, a piston and a piston rod, a passage, a needle valve and a stepping motor.
The cylinder is coupled to an outer tube. The piston is slidably inserted into the cylinder to partition the interior of the cylinder into a compression side chamber and an extension side chamber. The piston rod is inserted into the cylinder, one end is coupled to an inner tube slidably inserted into the outer tube and the other end is coupled to the piston.
The passage allows communication between the compression side chamber and the extension side chamber of the damper main body. A check valve is provided at an intermediate position of the passage and permits only a flow from the compression side chamber toward the extension side chamber or, conversely, a flow from the extension side chamber toward the compression side chamber. The needle valve is provided at an intermediate position of the passage. The stepping motor is fixed to an other end side of the piston rod and drives the needle valve.
This damper exerts a damping force by applying resistance to the flow of hydraulic oil by a piston valve provided in the piston at the time of extension and exerts a damping force by applying resistance to the flow of hydraulic oil leaking out from the cylinder to a reservoir by a base valve provided on an end part of the cylinder at the time of contraction.
In addition to this, the check valve permits the flow of hydraulic oil in the passage only at the time of extension or at the time of contraction and the needle valve applies resistance to the flow of hydraulic oil. Thus, the check valve and the needle valve exert damping forces in cooperation either at the time of extension or at the time of contraction of the damper. Further, the motor drives the needle valve, thereby making the damping force of the needle valve variable.
The needle valve fulfills a damping function only when the damper extends or contracts. Normally, a pair of left and right front forks is provided to suspend a wheel of the two-wheel vehicle. Thus, if the needle valve of the damper built in one front fork fulfills the damping function at the time of extension and the needle valve of the damper built in the other front fork fulfills the damping function at the time of contraction, the left and right front forks can adjust damping forces at extension and contraction sides as a whole.